Nitrocellulose plasticizer and pigment grinding composition



their surfaces by the grinding medium.

spatula.

Patented dune 211, i932 CARSON 3V. SIIiZI' /IS, WILLIAM J. BANNISTER,AND LLOYD C. SHALLEN, OF DEERE I-IA'UTE,

INDIANA, ASSIGNORS TO COMMERCIAL SQLVENTS CORPORATION, GE TEE/RE HAUIE,INDIANA, It. CQRPORATIQN OF LJIARYLAI'ID NITROCELL'ULQSE FLASTIGIZER ANDPEGMENT GRINDING COMPQSITION No Drawing. Original application filedFebruary filed February 10, 1830.

Our invention relates to certain improved plasticizing materials for usein the production of pigmented nitrocellulose co1npos1- tions, andpertains more especially to compositions comprising liquid non-volatileesters admixed with metal salts of half esters of phthalic acid. Suchsubstances, We have now discovered, are far superior to ordinaryplasticizers because of the superior pigmentwetting and pigment-grindingproperties which they possess.

The grinding of pigments for incorporation in nitrocellulose lacquers orpaints is ordinarily for the purpose of simply breaking down the aglomerates of pigment rather than for breaking down the pigmentparticles into still smaller subdivisions. The grinding simply breaksdown. the agglomerates so that the pigment particles may e wetted by thegrinding medium and the latter absorbed to disperse the pigment to asmooth paste. When the pigment used in a nitrocellulose lacquer or apaint has not been thoroughly ground, examination of the agglomeratedparticles indicates extremely dry surfaces which may cause settling ofthe pigment or other undesirable effects in the finished surface. Mostpigments resist the wetting of The measure of this resistance, which isprobably due to absorbed particles of air or gas on the pigmentparticles, is usually designated as the oil absorption number of thepigment.

In determining the oil absorption number of a pigment it is customary toproceed somewhat as follows: Twenty grams of the dry pigment are placedin a round. bottom glass vessel having dimensions of say i approximately2 diameter at the top, and

3 deep. The liquid to be used as a grinding medium is then added to thepigment from a burette. After each small addition of liquid the pigmentis well stirred with a VV'hen the pigment particles become Wet with theliquid, they tend to coalesce and form small lumps of paste whichincrease in size as the adsorption of liquid increases. When all of theremaining dry pigment has been picked up and wet, the end point isreached. This is indicated by the paste 92%, Serial No. 253,210. Dividedand this application Serial No. 227,420.

lumps becoming much softer and easily spread with the spatula. It shouldbe noted that the end point is usually Well defined and easilydetermined Within O.10.2 c. c. of the liquid used as the titratingmedium. Results are recorded as grams of liquid or oil required to justwet all of the particles of 100 grams of pigment.

The use of liquid non-volatile esters of phthalic acid, such as, forexample, the methyl, ethyl, propyl, butyl, amyl and heXyl esters ofphthalic acid as nitrocellulose solvents and plasticizers is Well knownin the art. Tie nitrocellulose plasticizing properties of alkyl estersof glyceryl and glycyl phthalic acid are also well known.

In Canadian Patent No. 260,927 of May 18, 1926, B. K. Brown and CharlesBogin have disclosed the use of certain metal alkyl resins as componentsof nitro-cellulose lacquer adapted to partly or completely displaceVarnish gums. These metal alkyl resins are more properly describable aspolyvalent metallic salts of alkyl half esters of phthalic acid. Thesecompounds are prepared by reacting an aqueous solution of the sodiumsalt of an alkyl half ester of phthalic acid with an aqueous solution ofa polyvalent metallic salt, whereupon, the desired compound isprecipitated. For example, the sodium salt of the monobutyl ester ofphthalic acid reacts with zinc chloride in accordance with the followingequation:

2 00,1311 0021311 1311020 come 2 CO2 Zn-OzC to form the zinc salt of themonobutyl ester of phthalic acid.

Salts of other polyvalent metals such as copper, lead, iron, manganese,nickel, cobalt, etc., give similar products Other allryl or aryl estersof phthalic acid ma" be employed. Altho there are naturally someexceptions to the general statement, these compounds may be generallycharacterized as solid, stable, neutral, resin-like substances,insoluble in water, soluble in organic solvents, and exerting a solventaction on nitrocellulose.

While both metal alkyl phthalates of the type described and liquidesters of phthalic acid such as diethyl, dibutyl, and diamyl phthalateshave been used in nitrocellulose lacquers for some time, we have nowmade the surprising discovery that the addition of a metal alkyl or arylphthalate to a phthalate ester produces a. remarkable change in itsphysical properties and greatly enhances its value for the purpose orpreparing pigmented nitrocellulose compositions. This new compositionnot only has a lower oil absorption number but also a pigment mixed withit has much greater fluidity than any other such composition that wehave examined. Pigments mixed with other materials which have beenemployed as grinding media form mixtures which are more plastic orputty-like and have little tendency to flow. Consequently, greatdifiiculty is experienced in causing the mixture of pigment and grindingmedium to flow thru the mill. The improvement obtained by the use of ourimproved plasticizer may be best illustrated by reference to the lacquercompounding processes now used in the art.

It is generally recognized that the phthalate esters are betterplasticizers than castor oil and other oily materials. Part of thissuperiority is due to the fact that the phthalate esters, unlike theoils, are solvents for nitrocellulose and hence are completely misciblewith nitrocellulose compositions. Another point of superiority is thestable character of the phthalates. Despite the generally admittedsuperiority of the phthalates, above mentioned, castor oil has continuedto be employed in the compounding of nitrocellulose lacquers, as apartial or complete substitute for true plasticizers, because of itssuperior properties in connection with the incorporation of pigments.

In the production of pigmented lacquers containing more than 1 pounds ofpigment per gallon, the proper grinding-of the pigment has been adifficult problem. For obvious reasons, the grinding of pigments involatile, inflammable solvents or solvent-nitrocellulose mixtures hasbeen impractical except by slow and expensive ball-mill grindin At thesame time, pigment grinding with true plasticizers as the wetting anddispersing agent has been difficult because of the large amounts ofplasticizer required to produce a mixture with the proper degree offluidity so that it will flow thru the mill. To impart the necessaryfluidity to the pigment it has been necessary to use a greaterproportion of plasticizer than is desirable in the finished lacquer andwith some materials even an excess of the plasticizer has not producedthe desired effect. For example, zinc oxide pigment and an amount ofdibutyl phthalate slightly in excess of the oil absorption value form aplastic-like mass which is very easily stirred with a spatula or paddlebut which, nevertheless, is passed thru the grinding mill only with thegreatest difliculty.

For the reasons which have just been enumerated, castor oil up to thepresent time has been largely used for the grinding of lacquer pigmentsand has thus found its way into nitrocellulose lacquers where it isotherwise inherently undesirable because of its instability and poorplasticizing qualities.

lVe have now discovered that if a small quantity of a metal alkyl oraryl phthalate is dissolved or dispersed in a phthalate ester such asdibutyl or diamyl phthalate, the plasticizing properties of the esterare in no way disturbed and that at the same time, the mixture haspigment-grinding properties that are even more eflicacious than thosepossessed by castor oil. The addition of the small quantity of metalalkyl or aryl phthalate to the pigment-grinding medium serves todecrease the oil absorption number of the lat ter to a point where it iscomparable with that of castor oil. Table I shows the effect on the oilabsorption number of pigmentgrinding media obtained by the addition of5% of zinc butyl phthalate to the latter. These values were obtained byfollowing the method described above, using zinc oxide as the pigment.Similar results were also obtained when other pigments such as carbonblack or chrome yellow were substituted for the zinc oxide.

lVe have found that in addition to lowering the oil absorption number ofa pigmentgrinding medium, the addition of such materials as metal alkylor aryl phthalates appears to have other desirable effects not clearlyshown by a determination of its oil absorption number. This is easilydemonstrable by comparing two samples of a particular pigment, one ofwhich has been mixed with castor oil and the other with our improvedplasticizing and pigment-grinding composition. The former is a purelyplastic body having no flow, while the latter is entirely viscous andhas excellent flowing qualities.

In comparing the relative merits of differ entpigment-grinding media, wehave found it convenient to modify somewhat the usual test fordetermining the oil absorption number of a pigment. Table II shown belowgives the results of a series of experiments made by weighing 10 gramsof zinc oxide onto a glass plate. Three cubic centimeters of the mediumto be tested was then worked into the pigment with a spatula. hen themixture being tested was thoroughly mixed with the pigment, theresultant mass was examined for its flowing qualities.

It was observed that generally the mixture of pigment and plasticizertook one of the following three forms:

1. Purely plastic body, having no fiow and very little cohesion.

2. Semi-plastic body having a much lower yield point than #1 butpossessing no flow. This form has a very high coefficient of cohesionand falls as a stringy mass when an attempt is made to pour it.

3. Purely viscous body having a zero yield point with a very highcoeliicient of cohesion. This material has excellent flowing qualitiesand falls from a spatula or container in the form of a very long,continuous stream.

The numbers used in the table below refer to the three forms which havejust been described. In certain cases the form of the mixture did notlend itself to definite classifications but was rather intermediatebetween two of the forms. In such cases, this form has been designatedby the numbers 1 or Similar results have been obtained when using otherpigments such as carbon black, titanox, lithopone, chrome yellow, etc.in place of zinc oxide.

We have found that the addition of approximately 5% of the particularmetal salt of the half ester of phthalic acid gives optimum results.Increasing the amounts up to about 5% shows a marked improvement in thepigment-grinding properties of the medium; beyond this point there isobtained a slight but not very marked improvement by further additions.

This is a division of our co-pending application, U. S. Serial No.253,210, filed February 9, 1928, for nitrocellulose plasticizer andpigment grinding composition.

Now having described our invention, we claim:

1. A process which comprises grinding a pigment in the presence of aliquid ester of phthalic acid and a metal salt of a half ester ofphthalic acid.

2. A process which comprises grinding a pigment in the presence of aliquid ester of phthalic acid containing about 5% of a metal salt of ahalf ester of phthalic acid dissolved therein.

3. A process which comprises grinding a pigment in the presence of aliquid dialkyl ester of phthalic acid and a metal salt of a halt esterof phthalic acid.

4. A process which comprises grinding a pigment in the presence of aliquid dialkyl ester of phthalic acid containing about 5% of a metalsalt of a halt ester of phthalic acid dissolved therein.

5. A process which comprises grinding a pigment in the presence ofdibutyl phthalate and a metal salt of a halt ester of phthalic acid.

6. A process which comprises grinding a pigment in the presence ofdibutyl phthalate containing about 5% of a metal salt of a half ester ofphthalic acid dissolved or dis persed therein.

7. A process which comprises grinding a pigment in the presence of aliquid ester of phthalic acid and a metal salt of the butyl half. esterof phthalic acid.

8. A process which comprises grinding a pigment in the presence of aliquid ester of phthalic acid containing about 5% of a metal salt of thebutyl halt ester of phthalic acid dissolved or dispersed therein.

9. A process which comprises grinding a pigment in the presence of aliquid ester of phthalic acid and zinc butyl phthalate.

10. A process which comprises grinding a pigment in the presence of aliquid ester of phtl alic acid containing about 5% of zinc butylphthalate dissolved or dispersed there- 1n.

11. A pigment grinding medium which comprises a liquid ester of phthalicacid and a metal salt of a half ester of phthalic acid.

12. A pigment grinding medium which comprises a liquid ester of phthalicacid con taining about 5% of a metal salt of a halt ester of phthalicacid dissolved therein.

13. A pigment grinding medium which comprises a liquid dialkyl ester ofphthalic acid and a metal salt of a halt ester of phthalic acid.

1 1-. A pigment grinding medium which comprises a liquid dialkyl esterof phthalic acid containing about 5% of a metal salt of a halt ester ofphthalic acid dissolved therein.

15. A pigment grinding medium which comprises dibutyl phthalate and ametal salt of a half ester of phthalic acid.

16. A pigment grinding medium which comprises dibutyl phthalatecontaining about 5% of a metal salt of a half ester of phthalic aciddissolved or dispersed therein.

17. A pigment grinding medium which comprises a liquid ester of phthalicacid and a metal salt or" the butyl halt ester of phthalic acid.

18. A pigment grinding medium which comprises a liquid ester of phthalicacid containing about 5% of a metal salt of the butyl half ester ofphthalic acid dissolved or dispersed therein.

19. A pigment grinding medium which comprises a liquid ester of phthalicacid and 5' zinc but-yl phthalate.

20. A pigment grinding medium which comprises a liquid ester of phthalicacid containing about 5% of zinc butyl phthalate dissolved or dispersedtherein.

In testimony whereof we affix our signatures.

CARSON W. SIMMS. LLOYD G. SXVALLEN. \VILLIAM J. BANNISTER.

